As is also known in the art, optical phased arrays (OPAs) allow electronic steering of lightwave beams with no moving parts. However, conventional OPAs have insertion loss and beam scanning speed characteristics which make them inappropriate for use in certain applications including directed energy applications, for example.
As is also known, advanced laser beam control by non-mechanical means is not currently used. Beam steering is typically done with mechanical ‘fast steering mirrors’ that are limited to bandwidths barely exceeding 1 kHz and agile switching times of several milliseconds. The performance of such mechanical beam steering systems seriously limits the degree of stabilization obtainable in electro-optic (EO) systems of all power levels. Such millisecond speeds are also inadequate for new applications, such as multi-target laser designation in which it is desirable to target substantially simultaneously multiple swarming vehicles (e.g. boats).
A recent DARPA development program, Adaptive Photonically Phase-Locked Elements (APPLE), aimed to improve the performance of non-mechanical beamsteering. Systems analyses of an APPLE beam director using standard optical phased arrays show scanning speeds and loss characteristics which are not suitable for desired applications. For example APPLE Phase 1 hardware using standard OPAs has a fill factor of about 0.4, which implies that only about 16% of the energy is coherently combined on a target. Furthermore, standard OPAs have a form factor that limit the fill factor of arrays of modules. Thus, in view of the above, it is understood that conventional fast steering mirrors are inadequate in all respects, and existing OPAs are only somewhat better.